Technical Field
The present invention relates to a fluorescent display tube in which electrons discharged by a filament-shaped cathodes are made to collide against an anode in an envelope held in a high-vacuum state to display luminously, and more particularly, to a fluorescent display tube having small power consumption of the cathodes.
Related Art
JP 3-65557 A discloses an invention of a fluorescent display device. This fluorescent display device includes an envelope whose interior is held in a high-vacuum state, an anode provided in the envelop, a control electrode provided above the anode within the envelope, and a plurality of filament-shaped cathodes whose both ends are supported by pairs of support bodies. The cathodes are stretched above the control electrode within the envelope. The electrons discharged from the cathodes are controlled by the control electrode by driving the electrodes, and the electrons are made to collide against the anode, thereby making a phosphor layer of the anode emit light. According to the invention of this fluorescent display device, pulse voltage is given to the plurality of connected cathodes, a scanning signal which is in synchronization with the pulse voltage is given to the control electrode, the scanning signal is distributed and supplied to the control electrode which is opposed to the anode corresponding to an end of the cathode during a top period of one cycle of the scanning signal. According to this, influence of end-cold phenomenon at the end of the cathode is avoided without shortening lifetime of the cathode, and a display area can be enlarged.
In the invention disclosed in JP 3-65557 A, as shown in FIG. 6 thereof, both ends of each of the connected plurality of cathodes 51, 52, . . . , 5n are connected to a cathode pulse driving circuit 25. Further, in the conventional technique of JP 3-65557 A, as shown in FIGS. 1 and 2, each of both ends of the plurality of filament-shaped cathodes 5 are respectively fixed to a pair of support bodies 4, 4, the pair of support bodies 4, 4 are air-tightly guided outside from the envelope and connected to an outside driving circuit, and driving voltage is given to the support bodies 4, 4.
FIG. 7 shows a configuration of a power source in the above-described conventional fluorescent display device together with a schematically illustrated electrode configuration. Here, the display pattern in the electrode configuration means a display area composed of the anode and the control electrode (grid). The above-described filament-shaped cathode (not shown) is stretched above the display area. A power source configuration which drives the electrodes includes a driver power source VH for giving driver voltage to the anode and the grid, a cathode power source Ef for giving cathode voltage to the cathodes, a logic power source VDD for giving logic voltage to operate a driving IC which drives the power sources of the electrodes by voltage, and a cutoff power source Ek for giving cutoff voltage. The cutoff voltage is potential to bring up potential of the cathodes to avoid a case where heat electron discharged from the filament-shaped cathodes reaches the anode and the grip when the driver power source is OFF and light is emitted.